Question about the Post 9/11 GI Bill and the Montgomery GI Bill...?

I dont know anything about the GI Bill or how it works, so id like to have a little bit of information before I go talk to the finance guys. I know that I signed up for the montgomery gi bill, payed the 100 bucks a month, the whole nine yards. Im REALLY interested in this post 9/11 gi bill though, and from what i heard its pretty much the greatest thing to happen to the military in years. My question is, do I automatically have the post 9/11 bill, or do i have to transfer it from my montgomery or something? Pretty lost in the sauce when it comes to this so any help would be appreciated. thanks.